Canadian-made Raleigh Sprites are quite a common sight on the streets of Toronto. The most popular colour seems to be black, but there are gorgeous candy apple red ones that I see quite often as well. The ladies Sprite had a true double-toptube Mixte frameset, very elegant and in contrast to the single sloping toptube of earlier Raleigh ladies models. The original configuration of the 1980s Sprites was a 5-speed complete with matching fenders and a classic Pletscher CS rack. This particular Sprite was my mom's, purchased sometime in the early-mid 1980s. She didn't ride it much and it spent most of its life in the musty basement of an old stone shed. It had some regular use sometime in the late-nineties to early-naughts by a family friend, who treated it to its only tune up. Sometime in the last decade the front wheel got smushed and it became officially derelict. I've had my eye on it for a couple of years as a new bike to build up for my wife.

Last spring, I pulled it out of the damp basement, stripped it of its old wheels, handlebars, brake levers, pedals and saddle, gave the frame a good cleaning and polished up the Shimano Tourney brakeset, SR Stem and Silstar crank arms with Simichrome. I then set to work with converting it to a 3-speed. I'm particularly fond of the Raleigh Superbe, and it is the Superbe's 3-speed/Dynohub combination that served as my inspiration for upgrading this Sprite.

First, I ordered a wheel set from Longleaf Bicycles, who provide a very high quality and inexpensive custom wheel building service. A Sturmey Archer SRF3 three-speed hub and Sanyo H27 dynamo hub are laced to Velo Orange 36 hole PBP rims. The only problem is that the original wheels were 27", causing a problem with brake reach for the handsome Shimano Tourney callipers on the rear wheel; they barely had enough reach with the original wheel diameter. Not wanting to have to purchase new longer reach brakes, I had my first part CNC-machined: a drop bolt to lower the rear brake so that its arms have enough reach:

Brake drop bolt for mixte frame

It works nearly perfectly and is very discrete:

Inconspicuous drop bolt

The only problem is that it takes up a bit of space that the fender could have used, resulting in a really tight fit. A future revision would have beveled the edge that comes into contact with the fender.

With the brake reach problem sorted, I went about setting up the handlebars (VO Tourist) with the 3-speed trigger shifter and brake levers. I tried the original levers but they didn't fit with the shifter. I had a pair of ridiculously expensive Paul Love Levers lying around from another project that fit perfectly:

3-speed trigger shifter with Paul Love Levers

The new Sturmey Archer 3-speed hubs feel and shift much better than the originals. I was able to run the shifter cables using the original bosses and did away with the plastic cover that comes with the new hubs:

I spent an evening mounting the lights and wiring them up. The matching taillight for the Sturmey Archer headlight was stolen, so I had to settle for a vintage Luxor taillight, which polished up to a near chrome-like finish. It's a surprisingly good looking match considering the Luxor is meant for a different era and style of cycling. In anticipation of using an original Sturmey Archer taillight, I made a wedge-based LED bulb, complete with copper heat sink. However, I decided to save that set for another project. The Luxor uses a threaded bulb, so I just made up an E10 copper-topped LED bulb with a red Cree XP-E. The XP-E, driven at ~500mA from the dynamo, is extremely bright, easily rivalling the current batch of boutique super bright battery taillights.

I had originally designed the circuit so a switch could select between flashing and solid modes, but it turned out that the Zener diode that needs to shunt the dynamo current during the off-cycle of the flash wasn't up to the task. I'm quite convinced of the value of flashing lights in urban settings, but in this case I've settled for solid lights while moving and a flashing standlight. The circuit has had a reasonable amount of bench testing on my dynamo testing jig, but it's now time to bundle it all into the lamp housing, put it on the bike and start riding with it. Here are a few pictures of the board with switch and copper heat sink mounted LED (described elsewhere):

The orignal selector switch on the top of the housing proved unreliable, so I enlarged an existing hole in the bottom of the housing to hold the switch, which has a nice rubber boot. Mounting the PCB was a little fiddly. A tiny L-bracket with one #4-40 tapped hole is used to mount the circuit board to the lamp housing:

The board looks like an odd fit, but that's because I made it as small as I possibly could, with the hope of fitting into smaller vintage lamp housings, such as the Luxor 65.

It all fits together nicely, with the retrofitted LED/heat sink/optics and switch looking fairly inconspicuous:

The taillight LED is ready to go, although I need to get the brown plastic taillight chromed (a gift from a generous reader!). I intend to save my really nice NOS SA lampset for some other project. Once the taillight is chromed (technically, vacuum metallized), I just need to hook up the taillight and dynamo wires and mount the lamps on the bike.

Future improvements could include a taillight flashing system, where the headlight is never disconnected from the dynamo, alleviating the problem of surging dynamo voltage when flashing both LEDs. I implemented this on a breadboard using a low-side N-FET to short the taillight LED, under the control of an Attiny10. This also has the advantage of smaller and fewer components than a 555-based flasher.

Another improvement I'd like to eventually make is to upgrade the optics. The headlight uses a Cree XM-L, which can take up to 3A of current. Unfortunately, small format narrow beam optics aren't yet available for the XM-L, but they are for its cousin the XP-G, whose 1A current maximum can easily handle the dynamo's output. The XM-L optic certainly improves the beam shape, but it still doesn't have as much throw as I would like. The best solution would be to fabricate a new heat sink for the XP-G and uses a narrower optic.

Thursday, April 12, 2012

While I patiently wait for the Bici LuxNº58A prototype to arrive from Australia, I've had some time to work on my wife's 'new' Raleigh Sprite Mixte. Her 1966 Superbe was heavy and very beaten up, so I decided to replace it with my Mom's mid 1980s Raleigh Sprite, which had been languishing in the garage for the better part of two decades. It cleaned up beautifully and the paint on the frame and fenders still looks great, with only a few scuffs and scrapes and no rust. I upgraded it with a new wheelset, including a Sanyo H27 hub dynamo from the nice gentleman at Long Leaf Bicycles. Despite the restoration being more of an upgrade to modern parts, I wanted to use an original Sturmey Archer lamp set (upgraded with modern LEDs, of course, both front and rear, and a standlight). My wife's old Raleigh Superbe had one of the nice Heron-style headset mounted lamp brackets. These are plentiful and can still be purchased as NOS:

Original Raleigh Heron bracket

A few weeks ago I finally got around to mounting the lamp set and started by popping off the stem, placing the bracket in the headset stack and slipping the lamp's bracket over the Heron mount. But, lo and behold, the bracket was too short, resulting in the butt of the lamp jammed up too close to the stem's handlebar mount. Turns out, the later model Sprite's used the modern forged aluminium quill stem, which is shorter and stubbier than the older chrome plated stems. The stubbier geometry was the problem and the original Heron bracket simply wasn't long enough.

Since the bike itself was free (thanks Mom!), I decided it would be worth investing a bit in getting the perfect lamp mounting solution. To accomodate the 700c wheel size, I'd already had a custom drop bolt for the rear brake machined anyway, so why not go to the trouble of custom fabricating another part? If that's not true love, I don't know what is.

I've been busy designing a sheet metal bracket for my headlamp prototype, so I thought I'd have a go at making a longer Raleigh-style headset mounted lamp bracket. My limited manufacturing experience has been restricted to CNC machining, so sheet metal design was new to me. Essentially, you design a flat part and then modify it by bending. If, like me, you're using cheapy prosumer CAD software, then the fabricator needs to 'unfold' your part to get a flat 2D profile again, which now accounts for the deformation caused by bending. This unfolded profile is laser cut and then bent on a press brake. Here's what I came up with:

First, the 2D profile:

and after bending and rendering:

The lightening bolt is, perhaps, an unnecessary frill, but I was inspired by the old JOS logo and couldn't resist. For fabrication, I used a nice place in Scarborough that was one of the few places that was happy to do a single piece for a reasonable price (in this case, I got two as they were unhappy with the forming marks on the first one they fabricated). Half of the places I emailed never got back to me, so kudos to Questa Design for working with the little guy. Here's the custom bracket compared to the original Raleigh Heron bracket:

Custom long bracket and Raleigh Heron headset mounted lamp brackets

Here it is mounted on the headset:

And with a vintage Sturmey Archer headlamp:

All seems well, although I need to get it chromed first before I finalize the installation. The only thing I'm a little worried about is how easily it will get knocked out of alignment. The orignal bracket had a keyway that interfaced with a groove in the fork thread to prevent rotation. The Sprite's fork thread has no such groove, so the only thing preventing rotation is the headset nut. Hopefully a bit of Loctite or maybe even a rubber washer will prevent unwanted rotation of the bracket.

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About Me

I really like bikes, especially old bikes from the 50s to the 70s. I'm oddly obsessed with dynamo powered bicycle lighting and vintage bicycle lamps and it is here that I try to reconcile these two obsessions. Contact me: jeffrey(dot)lee(at)gmail(dot)com